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A novel mathematical modeling has been proposed to generate synthetic vertical force signal induced by a single person jumping. This model can replicate much of the temporal and spectral features of the real jumping loading more reliably than the existing half-sine models coupled with Fourier series analysis. This includes lack of symmetry of individual jumping pulses and near-periodic nature of consecutive pulses. The model therefore offers way forward as to the development of a new generation of synthetic narrow-band jumping loads. In these, the shape and frequency content of the jumping force can be changed easily on a jump-by-jump basis, which simulates better on what is happening in reality during human jumping. The synthetic jumping loading can be used in assessing vibration serviceability of civil engineering structures for which such dynamic excitation is relevant, such as assembly structures and concert venues. DOI: 10.1061/(ASCE)EM.1943-7889.0000044 CE Database subject headings: Vibration; Excitation; Mathematical models; Dynamic models; Dynamic loads; Vertical loads.

This work analyses the accuracy and capabilities of two image-based tracking techniques related to digital image correlation and the Lucas–Kanade optical flow method, with the subsequent quantification of body motion in a fluid–structure interaction experiment. A computer-controlled shaker was used as a benchmark case to create a one-dimensional oscillatory target motion. Three target frequencies were recorded. The measurements obtained with a low-cost digital camera were compared to a high-precision motion tracking system. The comparison was performed under changes in image resolution, target motion and sampling frequency. The results show that, with a correct selection of the processing parameters, both tracking techniques were able to track the main motion and frequency of the target even after a reduction of four and five times the sampling frequency and image resolution, respectively. Within this good agreement, the Lucas–Kanade technique shows better accuracy under tested conditions, achieving up to 15.6% of lower tracking error. Nevertheless, the achievement of this higher accuracy is highly dependent on the position of the selected initial target point. These considerations are addressed to satisfactorily track the response of a wall-mounted cylinder subjected to a range of turbulent flows using a single camera as the measuring device. [ABSTRACT FROM AUTHOR]

Multi-segment models of the foot have been proposed in the past years to overcome limitations imposed by oversimplified traditional approaches used to describe foot kinematics, but they have been only partially validated and never compared. This paper presents a unique comparative assessment of the four most widely adopted foot kinematic models and aims to provide a guidance for the clinical interpretation of their results. Sensitivity of the models to differences between treadmill and overground walking was tested in nine young healthy adults using a 1D paired t-test. Repeatability was assessed by investigating the joint kinematics obtained when the same operator placed the markers on thirteen young healthy adults in two occasions. Reproducibility was then assessed using data from three randomly selected participants, asking three operators to repeat the marker placement three times. The analyses were performed on sagittal kinematics using curve similarity and correlation indices (Linear Fit Method) and absolute differences between selected points. Differences between treadmill and overground gait were highlighted by all the investigated models. The two most repeatable and reproducible investigated models had average correlations higher than 0.70, with the lowest values (0.56) obtained for the midfoot. Averaged correlations were always higher than 0.74 for the former and 0.70 for the latter, with the lowest obtained for the midfoot (0.64 and 0.51). For all investigated models, foot kinematics generally showed low repeatability: normative bands must be adopted with caution when used for comparison with patient data., (Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Because of inherent variability in all human cyclical movements, such as walking, running and jumping, data collected across a single cycle might be atypical and potentially unable to represent an individual's generalized performance. The study described here was designed to determine the number of successive cycles due to continuous, repetitive countermovement jumping which a test subject should perform in a single experimental session to achieve stability of the mean of the corresponding continuously measured ground reaction force (GRF) variables. Seven vertical GRF variables (period of jumping cycle, duration of contact phase, peak force amplitude and its timing, average rate of force development, average rate of force relaxation and impulse) were extracted on the cycle-by-cycle basis from vertical jumping force time histories generated by twelve participants who were jumping in response to regular electronic metronome beats in the range 2-2.8 Hz. Stability of the selected GRF variables across successive jumping cycles was examined for three jumping rates (2, 2.4 and 2.8 Hz) using two statistical methods: intra-class correlation (ICC) analysis and segmental averaging technique (SAT). Results of the ICC analysis indicated that an average of four successive cycles (mean 4.5 ± 2.7 for 2 Hz; 3.9 ± 2.6 for 2.4 Hz; 3.3 ± 2.7 for 2.8 Hz) were necessary to achieve maximum ICC values. Except for jumping period, maximum ICC values took values from 0.592 to 0.991 and all were significantly (p ≤ 0.05) different from zero. Results of the SAT revealed that an average of ten successive cycles (mean 10.5 ± 3.5 for 2 Hz; 9.2 ± 3.8 for 2.4 Hz; 9.0 ± 3.9 for 2.8 Hz) were necessary to achieve stability of the selected parameters using criteria previously reported in the literature. Using 10 reference trials, the SAT required standard deviation criterion values of 0.49, 0.41 and 0.55 for 2 Hz, 2.4 Hz and 2.8 Hz jumping rates, respectively, in order to approximate the ICC results. The results of the study suggest that the ICC might be a less conservative but more objective method to evaluate stability of the data. Based on these considerations, it can be recommended that a force time history due to continuous, repetitive countermovement jumping should include minimum of four (the average from the ICC analysis) and possibly as many as nine successive jumping cycles (the upper limit of the ICC analysis) to establish stable mean values of the selected GRF data. This information is important for both experimental measurements and analytical studies of GRF signals due to continuous, repetitive countermovement jumping. Key pointsThe number of successive jumping cycles due to continuous, repetitive countermovement jumping obtained from a test subject during in a single testing session influences the stability of the corresponding ground reaction force variables on a cycle-by-cycle basis.Researchers have used different criteria and methods for determining stability of ground reaction force data for a variety of activities, making comparisons among studies and activities difficult.In the present study, segmental averaging technique indicated that an average of ten successive jumping cycles were necessary to achieve stability of the selected force parameters using criteria previously reported in the literature, while less conservative test-retest intra-class correlation (ICC) analysis showed that an average of four successive jumping cycles were necessary for stability.Based on these considerations, it can be recommended that a force time history due to continuous, repetitive countermovement jumping should include minimum of four (the average from the ICC analysis) and possibly as many as nine successive jumping cycles (the upper limit of the ICC analysis) to achieve stability of jumping force data on a cycle-by-cycle basis.Knowledge about the stability of jumping force data is an important to maximize reliability of their experimental and analytical characterizations.